The long-term goal of this proposal is to understand the roles that Snail superfamily genes play during embryonic development in mammals. Snail superfamily genes encode zinc finger-containing DNA binding proteins that act as transcriptional repressors. This superfamily has two main branches: the Snail family and the Scratch family. Each branch of the Snail superfamily in vertebrates has two members: Snail and Slug for the Snail family, and Seratchl and Scratch2 for the Scratch family. We have been studying the Snail gene family members Sna and Slug, and have constructed and analyzed targeted null mutations of both of these genes. Sna homozygous mutant embryos die during gastrulation, exhibiting defects in the epithelialmesenchymal transition required for generation of the mesoderm. Slug homozygous mutant mice are viable, but show growth retardation and various other defects. However, many questions remain about the possible roles played by the Sna gene in developmental events occurring after gastrulation, or whether the Snail superfamily genes Scratchl and Scratch2 play essential roles during embryogenesis. In this proposal, both molecular and genetic approaches will be utilized to examine the roles that Snail superfamily genes play during embryogenesis in mice. The specific aims of this proposal are: 1) Construct conditional loss and gain of function alleles of the Sna gene to analyze its role during postgastrulation developmental stages; 2) Test the hypothesis that the roles of the vertebrate Snail and Slug genes have been interchanged during evolution from fish, amphibians and birds to mammals by constructing a knock-in allele of the Slug cDNA into the Sna locus; 3) Construct and analyze targeted null mutations of the Snail superfamily genes Scratch1 and Scratch2; 4) Examine the role of the Sna gene in development of the trophoblast cell lineage; 5) Identify downstream transcriptional targets of the Sna protein using microarray analysis of Sna mutant cell lines and embryos, in silico analysis of DNA binding sites, and DNA binding studies. These studies will further our understanding of the roles played by Snail superfamily genes during mammalian development, and will be relevant to the study of both normal and abnormal human development.